|  | 5.4 | IGRP Operation
| 5.4.1 | IGRP metrics
IGRP is a Cisco proprietary protocol and was developed to supercede RIP. IGRP is a distance-vector interior routing protocol. Distance-vector routing protocols call for each router to send all or a portion of its routing table in a routing update message at regular intervals to each of its neighboring routers. As routing information spreads throughout the network, routers can calculate distances to all nodes within the network. IGRP uses a combination of metrics. Network delay, bandwidth, reliability, and load are all factored into the routing decision. Network administrators can determine the settings for each of these metrics. IGRP uses either the settings determined by the administrator or the default settings of bandwidth and delay to automatically calculate the best routes. IGRP provides a wide range for its metrics. For example, reliability and load can have any value between 1 and 255; bandwidth can have values reflecting speeds from 1200 bps to 10 Gbps; and delay can have any value from 1 to 224 .Wide metric ranges allow an adequate metric setting in networks with widely varying performance characteristics. As a result, network administrators can influence route selection in an intuitive fashion. This is accomplished by weighting each of the four metrics--that is, telling the router how much to value a particular metric. The default values related to the weightings for IGRP give the most importance to bandwidth, which makes IGRP superior to RIP. In contrast, RIP does not weigh metrics because it only uses one--hop count.
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| IGRP Basics